U.S. patent application number 13/230437 was filed with the patent office on 2013-03-14 for point-to-multipoint simultaneous optical transmission system.
The applicant listed for this patent is Chen-Kuo Sun. Invention is credited to Chen-Kuo Sun.
Application Number | 20130064545 13/230437 |
Document ID | / |
Family ID | 47829941 |
Filed Date | 2013-03-14 |
United States Patent
Application |
20130064545 |
Kind Code |
A1 |
Sun; Chen-Kuo |
March 14, 2013 |
Point-to-Multipoint Simultaneous Optical Transmission System
Abstract
A point-to-multipoint optical communication network includes a
fiber optic cable, and a single photodiode for optical/electrical
conversion at the upstream end of the cable. On the other hand, an
"n" number of electrical/optical up-converters are connected
between an "n" number of downstream points and the downstream end
of the cable. Within this arrangement, radio frequency signals
"f.sub.n" from respective "n" different downstream points are
impressed onto respective wavelengths ".lamda..sub.n". The
resultant optical signals ".lamda..sub.n" can then be
simultaneously transmitted upstream over the fiber optic cable, and
passed through the photodiode for optical/electrical conversion and
transmission to an upstream point, according to "f.sub.n". For
downstream communications, a single transmitter and a single
wavelength .lamda. can be used to transmit all f.sub.n signals.
Inventors: |
Sun; Chen-Kuo; (Escondido,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Sun; Chen-Kuo |
Escondido |
CA |
US |
|
|
Family ID: |
47829941 |
Appl. No.: |
13/230437 |
Filed: |
September 12, 2011 |
Current U.S.
Class: |
398/70 |
Current CPC
Class: |
H04J 14/025 20130101;
H04J 14/0282 20130101; H04J 14/0298 20130101; H04J 14/0232
20130101 |
Class at
Publication: |
398/70 |
International
Class: |
H04J 14/00 20060101
H04J014/00 |
Claims
1. A system for simultaneously transmitting signals between a
single upstream point and a plurality of downstream points, wherein
the downstream points are individually numbered from "1" to "n",
and the system comprises: an optical fiber having an upstream end
and a plurality of downstream ends; a plurality of up-converters,
wherein each up-converter is connected to a respective downstream
end of the optical fiber at a respective downstream point for
impressing a radio frequency signal "f.sub.n" from the respective
downstream point onto a respective optical signal of wavelength
".lamda..sub.n" for a simultaneous upstream transmission of signals
"f.sub.n" from different downstream points "n" over the optical
fiber to the single upstream point; a single photodiode connected
to the upstream end of the optical fiber for simultaneously
receiving transmitted signals with wavelengths .lamda..sub.n from
the downstream points; and a down-converter connected to the
photodiode at the single upstream point for converting the radio
frequency signals "f.sub.n" from the respective wavelengths
".lamda..sub.n" for use at the upstream point.
2. A system as recited in claim 1 wherein the single photodiode has
a receive bandwidth and the wavelengths ".lamda..sub.n" are
individually and collectively within the receive bandwidth of the
single photodiode.
3. A system as recited in claim 1 further comprising a plurality of
down-converters connected to the photodiode at the single upstream
point, for segregating the signals "f.sub.n" from each other,
according to frequency.
4. A system as recited in claim 1 further comprising a downstream
transmitter connected to the upstream end of the optical fiber for
sending signals "f.sub.n" from the single upstream point to the
plurality of downstream points on a single optical signal of
wavelength .lamda., wherein the signals "f.sub.n" are routed at the
downstream end for further transmission to the particular
downstream points.
5. A system as recited in claim 4 further comprising a tuner at
each downstream point for selectively receiving the radio frequency
signal "f.sub.n" addressed to the particular downstream point.
6. A system as recited in claim 1 wherein
.lamda..sub.n=.lamda.+.DELTA..lamda..sub.n, and wherein each
.DELTA..lamda. is unique.
7. A system as recited in claim 1 wherein
.lamda..sub.n=.lamda.+.DELTA..lamda..sub.n, and wherein each
.DELTA..lamda. is equal to approximately 0.5 nm.
8. A system as recited in claim 1 wherein f.sub.(n+1)-f.sub.n is
equal to approximately 100 MHz.
9. A system as recited in claim 1 wherein n is an integer in a
range from 1 to 10.
10. A receiver for simultaneously receiving signals at a single
upstream point from a plurality of downstream points over an
optical network having a single optical transmission fiber with an
upstream end and a plurality of downstream ends, the receiver
comprising: a single photodiode for receiving light in a bandwidth
between a wavelength .lamda..sub.Lo and a wavelength
.lamda..sub.Hi, wherein the photodiode is connected to the upstream
end of the optical fiber for simultaneously receiving optical
signals .lamda..sub.n through the optical fiber from an "n" number
of different downstream points, wherein the wavelength
.lamda..sub.n is within the bandwidth from .lamda..sub.Lo to
.lamda..sub.Hi (.lamda..sub.Lo<.lamda..sub.n<.lamda..sub.Hi);
and a plurality of down-converters connected to the photodiode for
converting each .lamda..sub.n to a respective radio frequency
signal f.sub.n, and for segregating the signals f.sub.n according
to frequency at the single upstream point.
11. A receiver as recited in claim 10 wherein the network further
comprises an "n" number of up-converters, and wherein each
up-converter is connected to a respective downstream end of the
optical fiber at a respective downstream point for impressing a
radio frequency signal "f.sub.n" from the respective downstream
points onto a respective optical signal of wavelength
".lamda..sub.n" for a simultaneous upstream transmission of signals
"f.sub.n" from the different downstream points "n" over the optical
fiber to the single upstream point.
12. A receiver as recited in claim 10 wherein the network further
comprises a downstream transmitter connected to the upstream end of
the optical fiber for sending signals "f.sub.n" from the single
upstream point to the "n" number of downstream points on a single
optical signal of wavelength .lamda., wherein the signals "f.sub.n"
are routed at the downstream end for further transmission to the
particular downstream points.
13. A receiver as recited in claim 10 wherein the network further
comprises a tuner at each downstream point for selectively
receiving the radio frequency signal "f.sub.n" addressed to the
particular downstream point.
14. A receiver as recited in claim 10 wherein
.lamda..sub.n=.lamda.+.DELTA..lamda..sub.n, and wherein each
.DELTA..lamda. is unique.
15. A receiver as recited in claim 10 wherein
.lamda..sub.n=.lamda.+.DELTA..lamda..sub.n, and wherein each
.DELTA..lamda. is equal to approximately 0.5 nm.
16. A receiver as recited in claim 10 wherein
.lamda..sub.n=.lamda.+.DELTA..lamda..sub.n, and wherein each
.DELTA..lamda. is established to avoid overlaps between any two
different .lamda..sub.n and a consequent beating of the respective
signals.
17. A receiver as recited in claim 10 wherein f.sub.(n+1)-f.sub.n
is equal to approximately 100 MHz.
18. A method for simultaneously transmitting signals between a
single upstream point and a plurality of downstream points, wherein
the downstream points are individually numbered from "1" to "n",
and the method comprises the steps of: providing an optical fiber
having an upstream end and a plurality of downstream ends;
connecting each of a plurality of up-converters to a respective
downstream end of the optical fiber, wherein each up-converter is
connected at a different downstream point; impressing a unique
radio frequency signal "f.sub.n" at each different downstream point
"n" onto an optical signal of respective wavelength ".lamda..sub.n"
for a simultaneous upstream transmission of the signals "f.sub.n"
from the different downstream points "n" over the optical fiber to
the single upstream point; engaging a single photodiode with the
upstream end of the optical fiber, wherein the single photodiode
has a receive bandwidth between .lamda..sub.Lo and .lamda..sub.Hi,
and wherein the wavelengths ".lamda..sub.n" received by the
photodiode are individually and collectively within the receive
bandwidth of the photodiode
(.lamda..sub.Lo<.lamda..sub.n<.lamda..sub.Hi); using a
plurality of down-converters connected to the photodiode for
converting each .lamda..sub.n to a radio frequency signal f'.sub.n,
and for tuning the signals f'.sub.n according to frequency;
employing a downstream transmitter connected to the upstream end of
the optical fiber for a downstream transmission of signals
"f.sub.n" from the single upstream point to the plurality of
downstream points on a single optical signal of wavelength .lamda.;
routing signals "f.sub.n" at the downstream end for further
transmission to designated downstream points; and tuning the
signals "f.sub.n" at each designated downstream point for receipt
of the signal.
19. A method as recited in claim 18 wherein
.lamda..sub.n=.lamda.+.DELTA..lamda..sub.n, and wherein each
.DELTA..lamda. is unique.
20. A method as recited in claim 19 wherein each .DELTA..lamda. is
established to avoid overlaps between any two different
.lamda..sub.n and a consequent beating of the respective signals.
Description
FIELD OF THE INVENTION
[0001] The present invention pertains generally to optical
communications systems and networks. More particularly, the present
invention pertains to systems and networks that transmit radio
frequency signals "f", as optical signals ".lamda.", through
optical fibers. The present invention is particularly, but not
exclusively, useful as a point-to-multipoint network that
effectively accommodates a plurality of signals within a confined
bandwidth for simultaneous transmission on an essentially single
wavelength, optical signal.
BACKGROUND OF THE INVENTION
[0002] Many telecommunication networks typically function by
transmitting signals that are carried on radio frequency (RF)
waves. It is known, however, that such signals can also be
optically transmitted over glass fibers. Consequently, depending on
the particular application, and the economics that are involved, it
may be desirable to incorporate an optical transmission capability
within a communication network. When doing so, however, it is
desirable to optimize the use of glass fibers or, stated
differently, to use as few glass fibers as possible.
[0003] As a general consideration, in order to incorporate an
optical communication capability into a communication network, it
is first necessary to up-convert signals from a radio frequency
carrier "f" to an optical wavelength ".lamda.". Next, it is
necessary to introduce the optical signal into the upstream end of
an optical fiber cable. The optical signal is then transmitted over
the cable. At the downstream end of the cable, it is necessary to
down-convert the signal from its optical wavelength ".lamda." back
to the original radio frequency signal "f". In general, this works
fine for point-to-point communications (i.e. direct communication
from one point to another point). It can become problematical,
however, when more than two points at the same end of the optical
cable are involved at the same time.
[0004] One solution for using a single optical fiber in a network,
for the purpose of communicating between a single upstream point
[modem], and numerous downstream points [modems], has been to
employ a transmission protocol. Normally, such a protocol allows
the different points to queue in a manner that gives them
sequential access to the optical fiber. This obviously has its
limitations, as queuing often delays transmissions. An option here
is to incorporate more and different fiber optic cables. This,
however, can be costly.
[0005] In light of the above, it is an object of the present
invention to provide a point-to-multipoint optical communications
network that allows a plurality of downstream points to
simultaneously transmit optical signals to a single upstream point
using a same confined bandwidth, on a same optical fiber. Another
object of the present invention is to provide a system and method
for simultaneously receiving a plurality of optical signals over a
single optical fiber at a same point. Yet another object of the
present invention is to provide a point-to-multipoint optical
communications network that is easy to use, is simple to implement,
and is comparatively cost effective.
SUMMARY OF THE INVENTION
[0006] A system for simultaneously transmitting a plurality of
optical signals over a single optical fiber cable between a single
upstream point and an "n" number of downstream points is provided.
In particular, the present invention envisions there will be a
single point connected to the upstream end of the optical fiber,
and there will be an "n" number of points that are connected to a
respective "n" number of downstream ends of the optical fiber.
Typically, "n" will be an integer in the range from 1 to 10.
[0007] An "n" number of up-converters are required for use at the
downstream end of the optical fiber cable. Specifically, each of
these up-converters is connected to a downstream end of the optical
fiber between the optical fiber and a respective downstream point.
The purpose of these up-converters is to impress a radio frequency
signal "f.sub.n" from the particular downstream point onto an
optical signal of wavelength ".lamda..sub.n". The optical signal
".lamda..sub.n" will then be transmitted over the optical fiber
cable.
[0008] For the present invention, the radio frequency that is used
for the signal "f.sub.n" at each particular downstream point
[modem] will be specific for the particular point. Further, the
difference between frequencies (.DELTA.f), where
f.sub.n=f.sub.(n-1)+.DELTA.f.sub.n, may either be the same, or it
may vary to make it unique. Typically, each .DELTA.f will be in a
range between 50 MHz and 1 GHz. With this in mind, each radio
frequency f.sub.n is up-converted to a respective optical signal
.lamda..sub.n. Along with the frequency differences for f.sub.n,
the optical signals .lamda..sub.n will also differ. Specifically,
.lamda..sub.n=.lamda..sub.(n-1)+.DELTA..lamda..sub.n. In this
relationship, the difference in wavelength (.DELTA..lamda.) between
an optical signal .lamda..sub.n and .lamda..sub.(n+1) may either be
the same, or it may vary to make it unique. Typically, each
.DELTA..lamda. will be greater than approximately 0.5 nm. Despite
their differences, all of the optical signals .lamda..sub.n that
are to be simultaneously transmitted upstream through the optical
fiber will be within a relatively narrow bandwidth that extends
between .lamda..sub.Lo and .lamda..sub.Hi
(.lamda..sub.Lo<.lamda..sub.n<.lamda..sub.Hi).
[0009] As indicated above, there are an "n" number of downstream
points individually connected to the "n" number of downstream ends
of the optical fiber. Although there is only one upstream point,
there may be a plurality of modems. Consequently, it is necessary
there be only one receiver with only a single photodiode connected
to the upstream end of the optical fiber. Importantly, the
photodiode at the upstream point needs to accommodate the narrow
bandwidth between .lamda..sub.Lo and .lamda..sub.Hi
(.lamda..sub.Lo<.lamda..sub.n<.lamda..sub.Hi). For example,
if n=10 and .DELTA..lamda.=0.5 nm, the photodiode will need to
accommodate a 5 nm bandwidth. It will then be able to
simultaneously receive all signals transmitted on wavelengths
.lamda..sub.n from the various "n" downstream points.
[0010] A plurality of RF down-converters are connected to the
photodiode at the single upstream end of the optical fiber.
Specifically, these down-converters are provided to convert the
respective optical signal ".lamda..sub.n" to their respective radio
frequency signals "f.sub.n", and to segregate the signals "f.sub.n"
from each other for use at the upstream point, according to
frequency.
[0011] In order to provide for downstream communications over the
network, a single downstream transmitter is connected to the
upstream end of the optical fiber. Thus, signals "f.sub.n" from the
upstream point(s) are transmitted to the plurality of downstream
points on a single optical signal of wavelength .lamda.. The
signals "f.sub.n" are then routed at the downstream end for further
transmission to the particular downstream points. As an added
feature, each modem at the upstream point and each downstream point
may separately include a tuner for selectively receiving the radio
frequency signal "f.sub.n" addressed to the particular downstream
point.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The novel features of this invention, as well as the
invention itself, both as to its structure and its operation, will
be best understood from the accompanying drawing, taken in
conjunction with the accompanying description, in which similar
reference characters refer to similar parts, and in which the
FIGURE is a schematic presentation of the components required for a
system in accordance with the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0013] Referring to the FIGURE, a point-to-multipoint network in
accordance with the present invention is shown schematically and is
designated 10. As shown, the network 10 includes an "n" number of
upstream modems 12, and a same "n" number of downstream points
[modems] 14, of which the modems 12a, 12b, 12c, 14a, 14b and 14c
are exemplary. For the present invention, the number "n" may vary,
but it is anticipated to typically be an integer in the range from
two to ten. Thus, the upstream modem 12c and the downstream modem
14c each sequentially represent the possibility for a respective
third through tenth modem.
[0014] As shown in the FIGURE, the network 10 includes an optical
fiber 16 having an upstream end 18 and a downstream end 20.
Further, a wavelength-division multiplexer (WDM) 22 of a type well
known in the pertinent art is shown connected to the optical fiber
16 at its upstream end 18. Along with the WDM 22, there is a
transmit, electrical/optical up-converter 24 that includes a laser
diode. And, there is a receive, optical/electrical down-converter
26 that includes a photodiode. Using the upstream modem 12a as an
example, it will be seen that a radio frequency (RF) up-converter
27 and a transmitter 28 are connected with the modem 12a.
Specifically, within this combination, when a signal leaves the
modem 12a for transmission over the network 10, it leaves as an RF
signal with a frequency "f.sub.n". Thus, in the specific case of
modem 12a, this signal will be passed from the modem 12a to the
electrical/optical up-converter 24 as a downstream signal with the
frequency "f.sub.1" (i.e. n=1). Still referring to the upstream
modem 12a, it will be seen that this modem 12a also includes an RF
down-converter 29 and a receiver 30 that are connected with the
optical/electrical down-converter 26. Specifically, within this
combination, the modem 12a is set to receive an upstream signal
from the optical/electrical down-converter 26 that has an RF
frequency "f.sub.1". Recall from above, the modem 12a is only
exemplary. As intended for the present invention, the modems
12.sub.n will all function substantially the same, and each will
individually interact directly with the electrical/optical
up-converter 24 and the optical/electrical down-converter 26. The
only difference here will be that each modem 12.sub.n will be using
a different respective frequency "f.sub.n".
[0015] At its downstream end 20, the optical fiber 16 is connected
with an optical distribution network 32 that, in turn, is
separately connected to the various downstream points [modems]
14a-c. More specifically, the optical distribution network 32 is
directly connected to WDMs 34a, 34b and 34c via respective optical
fibers 35a, 35b and 35c. Further, each of the WDMs 34a, 34b and 34c
is connected to a respective electrical/optical up-converter 36a,
36b and 36c, as well as a respective optical/electrical
down-converter 38a, 38b and 38c. In turn, each of the
electrical/optical up-converters 36a, 36b and 36c is respectively
connected to a transmitter 40a, 40b and 40c with a respective RF
up-converter 41a, 41b and 41c. And, each of the optical/electrical
down-converters 38a, 38b and 38c is respectively connected to a
receiver 42a, 42b and 42c with a respective RF down-converter 43a,
43b and 43c.
[0016] An important aspect of the present invention concerns the
down-converter 26 and its photodiode that are connected with the
upstream end 18 of the optical fiber 16. Specifically, this single
photodiode (i.e. optical/electrical down-converter 26) is selected
to simultaneously accommodate several optical wavelengths (.lamda.)
that are within a relatively narrow bandwidth. Preferably, this
narrow bandwidth will be between a wavelength .lamda..sub.LO and a
wavelength .lamda..sub.HI, and will be approximately 5 nm.
[0017] In an operation of the present invention, all of the
downstream points [modems] 14a-c are able to simultaneously
transmit to a respective upstream modem 12a-c over the optical
fiber 16. By way of example, the modem 14c is chosen for disclosure
here as it is considered to be representative of all downstream
points [modems] 14. Accordingly, the designation "n" may be any
number, and it is used to apply to a particular downstream point
14. With this in mind, consider a radio frequency (RF) signal
"f.sub.n" that is created at the modem 14c. Once created, the
signal "f.sub.n" is sent by the transmitter 40c to the
electrical/optical up-converter 36c where it is converted from the
RF signal "f.sub.n" into an optical signal ".lamda..sub.n". WDM 34c
then passes the optical signal ".lamda..sub.n" to the optical
distribution network 32 for direct transmission over the optical
fiber 16, without delay. Along with this transmission of the
optical signal ".lamda..sub.n", also consider the possibility of a
radio frequency (RF) signal "f.sub.2" being simultaneously created
at the modem 14b. In this case, the signal "f.sub.2" is sent by the
transmitter 40b to the electrical/optical up-converter 36b, where
it is converted from the RF signal "f.sub.2" into an optical signal
".lamda..sub.2". WDM 34b then passes the optical signal
".lamda..sub.2" via the optical fiber 35b to the optical
distribution network 32 for direct transmission over the optical
fiber 16, together with any other optical signal
".lamda..sub.n".
[0018] In the above example, the RF signal "f.sub.n" (e.g. f.sub.3)
will be different from the signal "f.sub.2". Specifically, as
envisioned for the present invention, the difference between one
radio frequency "f.sub.n" and any other radio frequency in the
system (i.e. .DELTA.f=f.sub.(n+1)-f.sub.n) will be approximately
100 MHz. In a similar manner, there will also be a difference
between one optical signal and another (.DELTA..lamda.). In this
case a relationship is envisioned wherein
.lamda..sub.n=.lamda..sub.n-1+.DELTA..lamda..sub.n, with each
.DELTA..lamda. being predetermined. Specifically, each wavelength
difference .DELTA..lamda. may be unique or it may be relatively
constant. In any event, each .DELTA..lamda. is preferably greater
than approximately 0.5 nm. Importantly, in each instance, the
resultant .lamda..sub.n will be within the bandwidth between
.lamda..sub.LO and .lamda..sub.HI that is established by the
photodiode of optical/electrical down-converter 26.
[0019] At the upstream end 18 of optical fiber 16, as the optical
signals .lamda..sub.n (e.g. .lamda..sub.2 and .lamda..sub.3) are
received at WDM 22 they are sent to the down-converter 26 where
they are converted back to their original radio frequency
"f.sub.n". The radio frequency signals "f.sub.n" are then sent,
according to their RF frequency, to the appropriate receiver 30 of
upstream point [modem] 12 where they are processed.
[0020] For a downstream transmission of signals from the upstream
point [modem] 12 to the corresponding downstream point [modems] 14,
the nature of the single upstream point 12 allows for the more
traditional communication arrangement. In particular, only one
electric/optical up-converter 24 is needed, and all of the radio
frequency signals "f.sub.n" can be converted onto a same optical
signal wavelength ".lamda.". This optical signal ".lamda." is then
sent over the optical fiber 16, and is routed by the optical
distribution network 32 to a particular downstream point [modem]
14, according to the frequency "f.sub.n". Thus, at the
optical/electrical down-converter 38a, radio frequency signal
f.sub.1 will be routed to downstream point 14a. Similarly, radio
frequency signal f.sub.n will be routed to downstream point
14c.
[0021] While the particular Point-to-Multipoint Simultaneous
Optical Transmission System as herein shown and disclosed in detail
is fully capable of obtaining the objects and providing the
advantages herein before stated, it is to be understood that it is
merely illustrative of the presently preferred embodiments of the
invention and that no limitations are intended to the details of
construction or design herein shown other than as described in the
appended claims.
* * * * *